This invention relates in general to methods and means to breach or puncture sealed containers packed within a sealed storage drum such that gases formed within the sealed inner containers can be safely vented to remove the potential for development of explosive conditions due to the build-up of hydrogen gas within the drum. In particular, the invention relates to any such methods or means where the task is accomplished without requiring opening of the drum for removal and repackaging of the inner containers.
Hazardous wastes such as radioactive or chemical hazardous wastes, or in particular trans-uranic (TRU) wastes comprising radioactive elements, are currently typically disposed of by packing the wastes inside large drums, such as 55 gallon cylindrical plastic or metal drums, which are either closed in an air-tight manner such that no gases or other matter can escape from the containment, or are closed in a vented manner such that some gases are allowed to vent. In either case it is required that no radioactive material or substance can escape from the containment. The drums are then shipped to remote storage facilities for final storage, where they are stored underground or in specially designed structures. In many circumstances radiolysis (chemical decomposition brought about by radiation), chemical reactions or organic decomposition of the material placed within the drums creates hydrogen and/or other undesirable gases, resulting in a build-up over time of excessive amounts of hydrogen and/or other gases within the drum which if not addressed can lead to the formation of potentially explosive conditions. For example, it is potentially dangerous if the percentage of hydrogen gas exceeds five percent of the drum atmosphere. To address this serious problem, it is known to provide the storage drums with selective venting filters or other such devices which allow passage of hydrogen gases while retaining radioactive particulates within the drums. Unfortunately, many times the hazardous waste is first confined within inner layers of confinement, such as heat sealed, tied or knotted plastic bags made of relatively thin, flexible, relatively elastic, polyethylene (PE), polyurethane (PU) or polyvinyl chloride (PVC), cans or other rigid walled containers, or the like, which are then placed within the large drums, and a single drum will often contain multiple bags or other inner containers. Sometimes a quantity of hazardous waste is placed into two or more bags, with the first bag sealed and placed within the second, which is then sealed, etc. This results in an inner containment device with multiple layers of confinement. The drum itself forms the outer or primary layer of confinement and the inner containers form inner or secondary layers of confinement for the hazardous waste. Because the plastic bags and other inner containers are sealed and are by their nature impermeable to the gases which are formed over time, the gases are trapped and cannot pass through any venting devices provided for the drum, and undesirable or dangerous hydrogen gas build-up may occur within the drum.
In addition to the problem set forth above, some drums are provided with rigid internal polyethylene liners. In this case the drum forms the primary layer of confinement and the rigid internal liner forms a secondary containment layer. Likewise, the drums often contain sealed cans or other rigid wall containers and aerosol cans, and the gases present in these cans are not addressed by the known approaches.
Government transportation regulations promulgated by the Department of Energy, the Nuclear Regulatory Commission and other agencies require that where flexible inner layers of confinement are present within a drum, i.e., individual sealed bags or other containers, the amount of fissile hazardous material or the total waste wattage must be significantly limited in each drum. These regulations significantly increase shipping costs and require that excess amounts of fissile hazardous material or excess total waste wattage in a single drum must be repackaged into multiple drums. The current approach to this task involves opening the drums, physically breaching all the inner containers and then repackaging the containers within the drum or dispersing the containers into multiple drums. The bags cannot be merely punctured or slit, since the openings could be blocked upon repacking, resulting in entrapment of any new gases formed over time. Because of the hazardous nature of the materials involved, this process is extremely expensive due to the need to protect the workers from excessive exposure and due to the need to safely handle and isolate the hazardous materials from the environment during this operation, and costs for this type of operation can exceed $10,000 per drum. The amount of radioactive waste which can be put into a single drum having inner layers of confinement is severely restricted since the drum will have to be opened and processed. For example, 20 grams of plutonium waste may be confined within a single drum under the guidelines where no inner containers are present, but only 2 grams of plutonium waste is allowed if there are inner containers. There are currently an estimated 800,000 drums containing radioactive TRU waste which require venting and subsequent storage. Current regulations preclude transport of the drums unless the drums contain less than five percent hydrogen gas.
It is an object of this invention to provide a means to safely breach the inner containment layers within a larger containment drum at relatively low cost, without requiring the opening of the drum and the handling and repackaging of the inner containers. It is a further object to provide a means and method to perform this task which significantly reduces or removes worker exposure to the hazardous material, which can be performed at remote and various sites, which poses little or no threat for environmental release, which does not damage or degrade the drum, which does not cause chemical reactions within the drum, which functions on either PE, PU or PVC bags, which accounts for the problems created by rigid PE liners and sealed rigid-wall cans, and which breaches the inner containers in such manner that openings formed in the containers will not be blocked so that any gases which are produced over time subsequent to the initial venting and breaching operation will not be trapped by the inner containers but can be removed in routine manner by venting devices.
In general, the invention is a method and apparatus means for breaching and venting sealed inner containers contained within a larger storage or shipping drum, such as a 55 gallon plastic or metal drum, as well as the drum itself, without requiring the drum to be opened and the inner containers removed, breached and repacked. The total volume of the inner containers is typically 90 percent or less of the total drum volume, such that a void is present in the drum. In particular, the invention is a method and apparatus for breaching and venting inner containers consisting of thin-walled, flexible PE, PU or PVC bags which have been sealed, and which contain hazardous materials such as radioactive or chemical wastes. In a more preferred embodiment, the invention is also a method and apparatus for breaching and venting sealed cans, aerosol cans and the like in addition to the sealed bags.
The invention comprises providing a drum interior access means such as a venting mechanism device or fitting, preferably self-drilling, self-tapping and self-sealing, with a specialized filter to preclude passage of undesirable gases and particulates, which is inserted through the lid of the drum to create a communicating passageway to the interior of the drum, where the venting mechanism has suitable fluid communication passageways for evacuating, pressurizing or freezing the interior of the drum. The venting mechanism is connected to a vacuum pumping apparatus, such that a high vacuum can be pulled through the venting mechanism. The atmosphere within the drum is evacuated, causing the inner containers to expand and burst due to the pressure differential between the interior of the sealed bags and the evacuated interior of the drum. The atmosphere drawn from the drum may be returned to the drum after the inner containment layers have been breached and vented, or it may disposed of separately with ambient atmosphere or another gas supplied into the drum to normalize the internal pressure.
In a preferred embodiment, the invention further comprises providing a liquid nitrogen source and providing fluid communication means, preferably within the venting mechanism itself, to deliver liquid nitrogen into the drum in order to freeze the flexible bags prior to the drum evacuation step. This converts the bag compositional material from a flexible and elastic material to a brittle material, or at least a material of reduced elasticity, and is particularly efficacious when bags made of PVC form some or all of the inner containers. In an alternative embodiment, means to increase the pressure within the drum are provided, such as by the introduction of compressed air, and the method further entails increasing the internal drum pressure prior to evacuating the drum. Alternatively, various combinations of pressurization, evacuation and freezing steps may be utilized, and each step may be performed more than once.
In another preferred embodiment, a sealable secondary chamber is provided to receive and contain the drum during the various processing operations. This allows the pressure external to the drum within the secondary chamber to be controlled, such that the pressure differential between the interior of the drum and the exterior of the drum may be maintained within defined safe tolerances to prevent damage to the drum. The pressure within the secondary chamber may be controlled by a separate evacuation and pressurization means, or the venting mechanism may be provided with auxiliary conduit or valve means such that the pressure within the drum and within the chamber but external to the drum remain within the defined tolerances with the use of single evacuation and pressurization means.
In still another alternative embodiment, a secondary overpack drum is provided to receive the drum to be evacuated. A drum opening mechanism is provided in the lid or body of the overpack drum, such that the drum to be evacuated can be opened after the drum has been placed into the sealed overpack drum. A communication vent and filtering means are provided in the overpack drum. The drum and overpack drum are then placed into a conditioning chamber where the temperature is drastically reduced. The drum and overpack are then removed, and evacuation means are connected to the communication vent to evacuate the overpack drum and the drum, with resulting rupture of any inner containers.